The Collaborative International Dictionary of English v.0.48:

Dreissena \Dreis"se*na\, prop. n. [NL. Named after Dreyssen, a
   Belgian physician.] (Zool.)
   A genus of bivalve shells of which one species (Dreissena
   polymorpha) is often so abundant as to be very troublesome
   in the fresh waters of Europe.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Dreissena
    n 1: zebra mussels [syn: Dreissena, genus Dreissena]